proc 2/2: remove struct proc_dir_entry::owner

Setting ->owner as done currently (pde->owner = THIS_MODULE) is racy
as correctly noted at bug #12454. Someone can lookup entry with NULL
->owner, thus not pinning enything, and release it later resulting
in module refcount underflow.

We can keep ->owner and supply it at registration time like ->proc_fops
and ->data.

But this leaves ->owner as easy-manipulative field (just one C assignment)
and somebody will forget to unpin previous/pin current module when
switching ->owner. ->proc_fops is declared as "const" which should give
some thoughts.

->read_proc/->write_proc were just fixed to not require ->owner for
protection.

rmmod'ed directories will be empty and return "." and ".." -- no harm.
And directories with tricky enough readdir and lookup shouldn't be modular.
We definitely don't want such modular code.

Removing ->owner will also make PDE smaller.

So, let's nuke it.

Kudos to Jeff Layton for reminding about this, let's say, oversight.

http://bugzilla.kernel.org/show_bug.cgi?id=12454

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

drivers/net/bonding/bond_main.c

@@ -3444,25 +3444,12 @@ static void bond_remove_proc_entry(struct bonding *bond)
  */
 static void bond_create_proc_dir(void)
 {
-	int len = strlen(DRV_NAME);
-
-	for (bond_proc_dir = init_net.proc_net->subdir; bond_proc_dir;
-	     bond_proc_dir = bond_proc_dir->next) {
-		if ((bond_proc_dir->namelen == len) &&
-		    !memcmp(bond_proc_dir->name, DRV_NAME, len)) {
-			break;
-		}
-	}
-
 	if (!bond_proc_dir) {
 		bond_proc_dir = proc_mkdir(DRV_NAME, init_net.proc_net);
-		if (bond_proc_dir) {
-			bond_proc_dir->owner = THIS_MODULE;
-		} else {
+		if (!bond_proc_dir)
 			printk(KERN_WARNING DRV_NAME
 				": Warning: cannot create /proc/net/%s\n",
 				DRV_NAME);
-		}
 	}
 }
 
@@ -3471,25 +3458,7 @@ static void bond_create_proc_dir(void)
  */
 static void bond_destroy_proc_dir(void)
 {
-	struct proc_dir_entry *de;
-
-	if (!bond_proc_dir) {
-		return;
-	}
-
-	/* verify that the /proc dir is empty */
-	for (de = bond_proc_dir->subdir; de; de = de->next) {
-		/* ignore . and .. */
-		if (*(de->name) != '.') {
-			break;
-		}
-	}
-
-	if (de) {
-		if (bond_proc_dir->owner == THIS_MODULE) {
-			bond_proc_dir->owner = NULL;
-		}
-	} else {
+	if (bond_proc_dir) {
 		remove_proc_entry(DRV_NAME, init_net.proc_net);
 		bond_proc_dir = NULL;
 	}